In the field of vehicle control, by-wire systems are proposed which electrically control an actuator for changing vehicle conditions by a by-wire control circuit according to commands from a vehicle passenger. Examples of these by-wire systems include a drive-by-wire system (e.g., Japanese Patent Application No. 2005-133624A, U.S. Patent Publication No. 2005/0092292A1) that changes throttle openings of an engine according to commands from a vehicle passenger, a shift-by-wire system (e.g., Japanese Patent Application No. 2004-230952A) that changes ranges of an automatic transmission according to commands, and a steering-by-wire system (e.g., Japanese Patent Application No. 2004-268754) that changes steering angles of a vehicle steering shaft according to commands.
The drive-by-wire system described above can prevent a sudden engine stall by ensuring a minimum throttle opening by the mechanical workings of an engine, even when an actuator realizes a throttle opening contrary to the intention of a vehicle passenger.
On the other hand, in the shift-by-wire system described above, when a fault occurs and the actuator fixes a range that is contrary to the intention of the vehicle passenger, the vehicle may remain running, thereby creating a potential hazard. Likewise, in the steering-by-wire system, when a fault occurs and the actuator fixes the steering angle to an angle that is contrary to the intention of the vehicle passenger, the vehicle may remain running, thereby creating a potential hazard.